I have a matrix A and want to make QR Factorization: A= QR;
Then i want to solve the Q^T * unit_vector. vec = Q^T * vec;

I have a loop around this operation in which the A matrix which is an
double array changes as well as its dimension.

Now the problem:
For small input matrix A everythink works correct even if the number of loops within for-loop is very big > 1000.
For big input matrices A everything works correkt if the number of loop iterations is small < 30. But if set the iterations to e.g.: 35 than my programms get a segmentation fault within a blas routine. If I check this with valgrind i get several times the following output :

Can anybode tell me why my method with using dormqr doesn't work correctly? I would prefer avoiding this for-loop and using dormqr. But why the hell it doesn't work with the above code for huge problems?

The C code below seems to work fine. (Valgrind do not complain at least.)
What is your problem exactly?
(NB if you only have one vector on which you want to apply the Householder
reflection, then it makes sense to call DLARF directly.)

Hello,
Can you try to install BLAS and LAPACK by yourself?
o Download them from http://www.netlib.org/lapack/lapack-lite-3.1.1.tgzo Then untar,
o Edit the make.inc file with your compiler (there is a make.inc.example that should almost
do it)
o Type make blaslib then make lib
After this you'll have two .a files. (lapack and blas), a good idea is to rename as
libreflapack.a and librefblas.a
Link your application with these.
I am curious to see the result.
Julien.

First off all, very nice thread! it helped me solve an issue I had while using dlarf.

Is there something like a dormqr "lite" version? This is in the context of doing QR delete column block updates. Basically I need to apply a set of elementary reflectors compacted in matrix A starting from a column K and only a block close to a small band right below the diagonal, this small band is of width P (how many columns were deleted). See the code below which is an adaptation of http://www.maths.manchester.ac.uk/~cluc ... delcolsq.f in order to apply the elementary reflectors to an arbitrary matrix. My question is whether there exist a dormqr "lite" that could compute the same?